This invention relates to arc extinguishing structures for use in electrical switching devices. More particularly, this invention relates to arc chutes and cooperative venting arrangements in electric circuit breakers.
Arc extinguishing structures employed in molded case circuit breakers or other enclosed electrical switching devices are designed to draw the arc off the switch contacts, rapidly lengthen and fragmentize the arc to dissipate its energy, and to cool the arc associated ionized gases prior to venting the same to the atmosphere. Arc chutes have commonly been employed in devices of the aforementioned type to attract the arc from the contacts and rapidly lengthen and fragmentize it. These arc chutes comprise a plurality of metallic arc plates arranged in a spaced-apart relation along the path of movement of the separating contacts. The arc plates are mounted between a pair of insulating side plates and are assembled to the circuit breaker or switching device housing as a subassembly. The insulating housing of the circuit breaker or switching device is provided with one or more vent openings and passageways leading to the openings for exhausting the arc associated gases. The passageways and vent openings are commonly provided with one or more mesh screens or perforated plates to provide a plurality of surfaces against which the ionized gases may strike and be deflected, thereby cooling and deionizing the gases. Such screens and plates also prevent the direct insertion of a tool or other object into the switching device to interfere with switching operations. However, these additional screens and perforated plates restrict the flow of gas from the housing, thereby creating back pressure at the arc plates which inhibits entry of the arc to the plates, and increased internal pressure which may be harmful to the switch housihg. Moreover, these additional screens and perforated plates increase the manufacturing assembly cost of the switching device.